It is known to provide body electrodes for electromedical use comprising a conductive metal plate having a terminal by means of which it can be electrically connected to the electro-surgical unit, and a layer of fibrous material wetted or impregnated with a liquid or semi-solid conductive medium, the inner surface of which is adapted to contact the patient's skin and the outer surface of which contacts the surface of the metal plate. It is very important, in electro-surgical procedures, that the body electrode contact the patient's skin in electrically conductive manner over a substantial area, so as to distribute the electric current over a sufficiently large area to eliminate excessive heating effects.
It is also important to avoid direct contacts of the metal plate and the patient's skin, since this is likely to cause burning of the patient's skin. The electrical conductivity achieved between a conductive metal plate and a patient's skin is too low to permit passage of electric currents of the magnitude used in electro-surgical techniques therebetween without serious resistive heating effects, resulting in burns to the patient's skin. Very high frequency, high voltage alternating electric currents are used in electro-surgical techniques. The provision of a conductive medium, such as a conductive gel, liquid, cream or paste, between the metal plate and the patient's skin, is thus very important. The conductive medium is generally water based, and contains electrolytes, and has the ability to penetrate the skin to some extent to provide an electrically conductive path from the patient's body to the metal plate, of low electrical resistance. The skin is a generally non-conductive, dielectric material, and by penetrating the skin the conductive medium provides an electrically conductive path through the skin.
It will thus be appreciated that the conductive medium has an important role to play in the satisfactory performance of any return body electrode. If the electrode is to perform satisfactorily, not only must the conductive medium be of high electrical conductivity and be able to penetrate the patient's skin to the correct degree to provide the low electrical resistive return path to the metal plate, but also the conductive medium must be held in the right location relative to the metal plate. It must extend over the whole area of the metal plate, so that the electric current is distributed over the whole area. It must be held so that, during use, it does not run out or become squeezed out from between the metal plate and the skin when the electrode is tightly affixed to the body, even when the electrode is disposed vertically. It must not dry out prior to or during use, after application to the electrode, so as to reduce its electrical conductivity. Moreover, it should provide a thin conductive layer of essentially uniform thickness between the metal plate and the skin, for best distribution of current over the area of the electrode.